Procedure for igniting thick, carbonaceous formations



June 28, 1966 D. R. PARRISH 3,258,073

PROCEDURE FOR IGNITING THICK, CARBONACEOUS FORMATIONS Filed Dec. 26, 1963 i? I g a a VN W Y,

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ATTORNEY United States Patent 3,258,073 PROCEDURE FOR IGNITING THICK, CARBONACEOUS FORMATIONS David R. Parrish, Tulsa, Okla, assignor to Pan American Petroleum Corporation, Tulsa, Okla, a corporation of Delaware Filed Dec. 26, 1963, Ser. No. 333,503 6 Claims. (Cl. 166-11) The present invention relates to the underground combustion of carbonaceous deposits. More particularly, it is concerned with a novel method for ignitingdeposits of this type that are relatively thick, i.e., from about 50 to I about 400 feet in thickness.

Briefly, this is accomplished, in accordance with my invention, by first igniting the lowermost 30 to 40 feet of oil sand penetrated by a cased well that has been perforated only over said lowermost 30 to 40 feet. The section opposite this perforated portion of the casing is then ignited in accordance with any of several known ignition procedures, for example, as described in copending application Serial No. 271,262, filed April 8, 1963, by Karol L. Hujsak. Once this section of formation is ignited, the next 30 or 40 feet of easing up the well is similarly perforated. The igniter is then repositioned opposite this second perforated section, or slightly above. At this level, a little more heat than is customary for a single ignition is used. Ordinarily, one million B.t.u. per vertical foot of formation face is considered adequate. However, in this case 1.25 million B.t.u. per foot of depth is considered preferable. The total heat input to a 40-foot section, then, would be represented by 40 1.25 million B.t.u. The entire formation, which may be much as 400 or 500 feet thick, can be ignited in this stepwise fashion.

Carbonaceous materials, such as heavy oils and tars, are frequently found in extensive layers or zones rang- 3,258,073 ?atented June 28, 1966 FIGURE 3 shows an injection well and a producing well both of which penetrate said oil-bearing section, said well being a part of an underground combustion project feet thick. A section of casing approximately 30 feet ing from a few feet to several hundred feet in thickness.

Ignition of the thin layers or deposits, i.e., up to about 30 or 40 feet thick, generally offer relatively little difficulty when employing current ignition techniques and available ignition equipment. However, in the case of such deposits substantially thicker than 40 feet, the heat (hot combustion products) from the igniter tends to flow into the more permeable sections, resulting in an uneven ignition of the formation face. If the injection of air is continued, further combustion, of course, occurs but in the form of an uneven and sometimes broken front moving from the injection well toward the producing well. As a result, the less permeable sections containing oilor tar are left unburned. Also, it frequently happens that the upper oilbearing sections are more permeable than those farther down the well bore. Accordingly, under such circumstances, the hot combustion gases from the burner tend to flow into the upper, more permeable levels, leaving the lower sections substantially unaffected.

Accordingly, it is an object of my invention to provide a method by which petroleum-bearing formations in excess of about 40 feet in thickness can be ignited to produce a substantially uniform combustion front throughout the entire depth of such formations. It is a further object of my invention to ignite thick oilor tar-bearing formations of the type contemplated herein by a stepwise ignition procedure, starting at the lower-most level of said formations and progressing up the well bore in substantially equally spaced intervals.

FIGURE 1 is a cross-sectional View of a cased well showing igniter equipment therein and perforations that have been made over the lowermost 30-foot portion of a 450 foot thick oil-bearing section.

FIGURE 2 is a cross-section of the same well shown in FIGURE 1, demonstrating the next step of ignition.

long located at the base of oil-bearing formation 4 is perforated to produce a first set of perforations 6. Igniter equipment is then lowered into the well down to a level preferably a few feet above the uppermost of perforations 6. Such equipment comprises essentially a fuel line 8, having affixed to the lower end thereof a burner 10. In one particular design of burner the air required for combustion is introduced through line 12 and into the well annulus where a portion thereof enters the top of burner 10, causing combustion with the fuel. The air bypassing the burner is used to ignite the formation once the latter has been brought to the proper temperature level. The burner is allowed to operate at the level shown in FIG- URE 1 until a space some three to four feet away from the Well is burning. This may require a period of from 3 to 5 days with the total heat input of about 1.25 million B.t.u. per vertical foot of formation. When the formation has thus been ignited, a burning area 14, such as is shown in FIGURE 2, is formed. Thereafter, additional perforations 16 are made in the casing over the next 30 feet thereof and immediately above ignited portion 14. Burner 10 is then raised to the elevation shown, and the ignition process is repeated to enlarge burning area 14 to that illustrated in injection well 18 of FIG- URE 3. entire 450 feet of formation have been ignited and are burning. Thereafter, the burner is removed and air injection continued into well 18 via line 19, whereby combustion zone 14 moves toward production well 20, causing oil to flow into well 20 through perforations 22 and eventually being produced therefrom via line 24.

In situations where the casing in the well to be ignited is already perforated, a squeeze cementing job can be done, preferably with a temperature-resistant cement, and the well perforated in accordance with my invention, after first drilling out the set cement remaining in the well bo're. Also, if it is found that lower sections of the well are taking an unduly large portion of the injected ignition gases, the portion of the well bore opposite the formation already ignited can be filled with sand. The sand serves to block the flow. of said gases into the lower sections and can easily be removed by the circulation of water or air after ignition of the entire formation face has been completed. Alternatively, straddle packers, which may be, for example, from 50 to 350 feet in length, can be used to temporarily block off the perforations above those into which hot combustion gases are initiallydirected. Thereafter, the packers can be moved up the well in 30 to 40 foot intervals and ignition effected as described. Likewise, packers of this type may be used in a relatively uniform open hole and the formation ignited in stepwise fashion in accordance with my invention. The lowermost packer is preferably of fireor heat-resistant construction.

It'will be appreciated that the principles of my invention may be applied to advantage in an arrangement of wells much more complex than that illustrated. The fact The ignition procedure is repeated until the to be stressed herein is that this invention concerns a method for igniting any thick petroleum-bearing formation. In this connection it should be pointed out that the ignition method of my invention can be used in cases where the formation of interest is to be subjected to reverse combustion and, accordingly, I do not limit myself to applications of this ignition process for use in conjunction with forward combustion projects. Also, this ignition is, likewise, applicable to thick sections of oil shale, coal, bituminous sands, etc., as well as oil-bearing formations suitable for combustion.

The term thick, as used herein in reference to a carbonaceous oil-bearing formation, is intended to mean a formation in excess of about 40 feet in thickness. The term carbonaceous, as used herein, is intended to refer to materials comprising either free or combined carbon.

I claim:

1. In a process for igniting a thick, carbonaceous deposit, said deposit being adapted to underground combustion and penetrated by a producing well and an injection well, the improvement comprising first igniting the lowermost section of said deposit penetrated by one of said wells, said section being not more than about 30 to 40 feet in thickness, and thereafter, but prior to effecting combustion and propagating the resulting combustion front through said deposit to recover valuable products therefrom, proceeding up said one of said wells in substantially equally spaced intervals of not more than about 40 feet until the entire face of said deposit has been ignited, thereby forming a combustion front coextensive with the thickness of said deposit adjacent said one of said wells.

2. The method of claim 1 in which the ignition process is effected in said injection well.

3. The method of claim 1 in which the ignition process is effected in said production well.

4. In a process for igniting a thick, carbonaceous deposit, said deposit being adapted to underground com bustion and penetrated by a production well and a cased injection well, the improvement which comprises first perforating the lowermost section of the casing in said injection well, said section being not more than about 30 to 40 feet in thickness, igniting said deposit opposite the resulting set of perforations, next perforating a second section of said casting adjacent said previously perforated section, having a thickness not in excess of the first perforated section, next igniting said deposit opposite said second section of said casing, and, prior to effecting combustion and propagating the resulting combustion front through said deposit, repeating the above cycle until said deposit has been ignited throughout its depth, thereby forming a combustion front coextensive with the thickness of said deposit adjacent said injection well.

5. In a process for igniting a thick, carbonaceous deposit, said deposit being adapted to underground combustion and penetrated by perforated, cased injection and production wells wherein the perforations in the casing of said injection well extends for an interval in excess of 30 to 40 feet opposite said deposit, the improvement which comprises first plugging said perforations in one of said wells, next perforating the lowermost section of said one of said wells, said section being not more than about 30 to 40 feet in thickness, igniting said deposit opposite the resulting newly perforated section, thereafter perforating a second section of the casing in said one of said wells adjacent said section that was previously perforated, said second section having a thickness of not more than about 30 to 40 feet, next igniting said deposit opposite said second perforated section of said casing, and, prior to effecting combustion and propagating the resulting combustion front through said deposit, repeating the above cycle until said deposit has been ignited throughout its depth, thereby forming a combustion front coextensive with the thickness of said deposit adjacent said injection well.

6. In a process for igniting a thick, carbonaceous deposit, said deposit being adapted to underground combustion and penetrated by a producing well and an injection well, the improvement comprising first the step of igniting the lowermost section of said deposit penetrated by one of said wells, said section being not more than about 30 to 40 feet in thickness, and thereafter, but prior to effecting combustion and propagating the resulting combustion front through said deposit, proceeding up said one of said wells with such ignition step in substantially equally spaced intervals of not more than about 40 feet, thereby forming a combustion front coextensive with the thickness of said deposit adjacent said injection well.

References Cited by the Examiner UNITED STATES PATENTS 2,877,847 3/1959 Pelzer et al. 16639 2,914,309 11/1959 Salomonsson 166-11 X 2,973,813 3/1961 Parker 1661l 3,004,594 10/1961 Crawford 166l1 3,138,203 6/1964 Weiss et a1. l66l1 X CHARLES E. O'CONNELL, Primary Examiner.

S. J. NOVOSAD, Assistant Examiner. 

1. IN A PROCESS FOR IGNITING A THICK, CARBONACEOUS DEPOSIT, SAID DEPOSIT BEING ADAPTED TO UNDERGROUND COMBUSTION AND PENETRATED BY A PRODUCING WELL AND AN INJECTION WELL, THE IMPROVEMENT COMPRISING FIRST IGNITING THE LOWERMOST SECTION OF SAID DEPOSIT PENETRATED BY ONE OF SAID WELLS, SAID SECTION BEING NOT MORE THAN ABOUT 30 TO 40 FEET IN THICKNESS, AND THEREAFTER, BUT PRIOR TO EFFECTING COMBUSTION AND PROPAGATING THE RESULTING COMBUSTION FRONT THROUGH SAID DEPOSIT TO RECOVER VALUABLE PRODUCTS THEREFROM, PROCEEDING UP SAID ONE OF SAID WELLS IN SUBSTANTIALLY EQUALLY SPACED INTERVALS OF NOT MORE THAN ABOUT 40 FEET UNTIL THE ENTIRE FACE OF SAID DEPOSIT HAS BEEN IGNITED, THEREBY FORMING A COMBUSTION FRONT COEXTENSIVE 